cmdeploy: run apt update to make sure dns-utils can be installed

CHANGELOG.md

@@ -2,6 +2,9 @@
 
 ## untagged
 
+- If `dns-utils` needs to be installed before cmdeploy run, apt update to make sure it works
+  ([#560](https://github.com/chatmail/relay/pull/560))
+
 - Add config value after how many days large files are deleted
   ([#555](https://github.com/chatmail/relay/pull/555))
 

cmdeploy/src/cmdeploy/remote/rdns.py

@@ -19,7 +19,7 @@ def perform_initial_checks(mail_domain):
     """Collecting initial DNS settings."""
     assert mail_domain
     if not shell("dig", fail_ok=True):
-        shell("apt-get install -y dnsutils")
+        shell("apt-get update && apt-get install -y dnsutils")
     A = query_dns("A", mail_domain)
     AAAA = query_dns("AAAA", mail_domain)
     MTA_STS = query_dns("CNAME", f"mta-sts.{mail_domain}")